Synopsis Other Factual Information Witnesses at the accident site reported that, at the time of the accident, the sky was clear and there were light winds from the southwest. The pilots were certified and qualified for the flight in accordance with the Transport Canada (TC) Ultralight Aeroplane Policy. The right seat position was occupied by the qualified ultralight instructor. The left seat position was occupied by the commercial ultralight student, who was also the owner. A witness reported that he was in attendance during the pre-flight briefing and that he overheard the pilots discussing their intention of practicing unusual attitudes and spins during the upcoming flight. The aircraft is not approved for spins. The aircraft was manufactured in 1985, and the owner purchased it, ready to fly, in May 1995. No maintenance history of the aircraft was found; however, a sales receipt and TC registration form indicate that the aircraft was recently re-equipped from a 50 hp (Rotax model 502 GU) to a 65 hp (Rotax model 582) engine. The Cuby II aircraft is a two-place, side-by-side, high-wing, conventional-gear monoplane. The designer's sketch specifies the cross-sectional dimensions of the spar caps as follows: the top main wing spar caps are to be constructed of 1 inch high by inch wide Sitka spruce; the lower spar caps are to be 1 inch high by inch wide, and also of Sitka spruce. The main spar caps are to be joined by inch wide Douglas fir shear webbing. The wreckage examination revealed that the outer section of the left wing was missing from the main wreckage, and was located in a field about 279 feet to the northeast. Other pieces of fabric and aluminum ribs from the left wing were strewn in a northeast direction up to a maximum distance of about 1,740 feet from the main point of impact. The left wing wooden front and rear spars were found with a vertical break near the lift strut attachment fittings. Examination of these surfaces by the TSB Engineering Branch determined that the fractures were a result of compression damage. There was no evidence to indicate that the left wing spars had been replaced since original manufacture in 1985. Examination of the aircraft's failed left wing spars indicated that they were not constructed in accordance with the designer's sketch. The wood grain orientation of the failed spar caps was found to be at 90 degrees to the direction recommended and was unsatisfactory for straightness. The spar caps and webs were under-dimensioned; 3/16 inch mahogany had been substituted for the inch fir plywood shear web called for in the sketch. In addition, the spar cap wood material was fir and not sitka spruce, as specified. Further examination reveals that the structural stability of the aircraft's wing design was questionable. Any sort of aerobatic manoeuvre, particularly ones requiring positive high angles of attack for entry, would be hazardous. There was also evidence of previous damage to the left wing in the form of a left wing tip spar and fabric repair. There were no wing inspection ports to allow for adequate periodic inspections of the internal wing structure. The effect of the spar failure on the flight characteristics of the aircraft would be such that the left wing would experience a loss of lift, and that the aircraft would enter an uncommanded roll to the left. Ultralight aeroplanes are exempt from airworthiness certification requirements, and neither a Certificate of Airworthiness (C of A) nor a Flight Permit is required. At the time this aircraft was built, there were no TC-regulated design, construction, or assembly standards established for ultralight aircraft. There are now TC design standards for advanced ultralight aircraft. The current Cuby II is designated as an advanced ultralight and must meet these design standards. The engine was examined, and no evidence of any pre-existing malfunction was found. The lack of propeller blade damage was consistent with reduced power being produced at the time of impact. An examination of the flight control system did not indicate any discontinuities, and all controls were capable of normal operation. Gap seals were not installed between the trailing edge of the wing and the leading edge of the ailerons. The manufacturer advises that tape gap seals reduce turbulence around the ailerons and improve the lateral stability of an aircraft. The magnetos and key were found in the OFF position. There were two fuel tanks installed: one in the right wing and one behind the front seats. In addition, a plastic five-Imperial-gallon fuel container was located in the baggage compartment. All were ruptured and contained residual fuel. The ground, at the point of main impact, was saturated with fuel. The centre of gravity (C of G) and wing loading could not be calculated because of the undetermined amount of fuel on board. However, considering the weight of both pilots, the additional weight of the newly installed engine, and the fuel-saturated ground, it is possible that the aircraft was at the maximum allowable weight and wing loading. An autopsy of the deceased pilots by the Provincial Medical Examiner revealed that the cause of death has been attributed to multiple blunt injuries. The accident was not survivable because of the high deceleration forces and the destruction of the front of the cockpit. Postmortem toxicology of the instructor revealed the presence of tetrahydrocannabinol (Cannabis-containing substance) within the blood. During the field investigation, a marijuana cigarette was found in a cigarette package located in the cockpit.